allow div-by-zero in shadow utils

Bug: oss-fuzz:6665
Change-Id: I5cbe02bf574d849340c85c0964d92ece45daac1f
Reviewed-on: https://skia-review.googlesource.com/129932
Commit-Queue: Mike Reed <reed@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Auto-Submit: Mike Reed <reed@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
1 file changed